1. Field of Invention
The invention relates to charged particle beam columns and in particular to charged particle beam columns that generate variable shaped beams.
2. Related Art
It is well known in the field of electron beam pattern generation that it is desirable to increase the throughput of pattern generation systems. The two main applications for such pattern generation systems are mask making for use in photolithography semiconductor fabrication and direct writing of patterns onto wafers to form semiconductor devices.
Lithographic systems typically used in electron beam pattern generation generate or expose patterns by controlling the flow of energy from a source to a substrate coated with a layer sensitive to that form of energy. Pattern exposure is controlled and partitioned into discrete units commonly referred to as flashes, wherein a flash is that portion of the pattern exposed during one cycle of an exposure sequence. Flashes are produced by allowing energy from the source, for example light, electron or other particle beams, to reach the coated substrate within selected pattern areas. The details of flash composition, dose and exposure sequence used to produce a pattern, and hence the control of the lithographic system, define what is known as a writing strategy.
In a typical vector scan writing strategy, the beam is positioned only over those sites that require exposure and then unblanked to expose the site (xe2x80x9cflashxe2x80x9d). Positioning is accomplished by a combination of substrate stage and beam movement in what is often referred to as a semi-random scan. Thus, pattern data must be provided that includes both the dose and position of each flash or site exposed. Frequently, vector scan strategies use a variable shaped beam, that is a beam capable of having a different size and/or shape (in terms of cross section) for each flash. The pattern is then composed from these variable shapes, called primitives. A shaped beam is capable of exposing a so called primitive. Where a variable shaped beam is used, the data additionally includes the location, size and shape for each flash.
The typical vector scan process decomposes patterns into rectangular shaped primitives. These rectangles are aligned along the x-y axes defining the vector scan. Thus for example in the pattern depicted in FIG. 1, using a typical vector scan process, only five sub-patterns are true rectangles while the other 62 sub-patterns are triangles approximated by multiple small rectangles. As shown in the example, in a conventional vector scan process, while only 17% of the pattern consists of slanted lines, patterning the slanted lines, i.e., sides not parallel to the x-y vector scan grid, using the rectangle approximations takes approximately 90% of the exposure time.
Techniques to generate shaped beams using multiple openings defined in a single aperture are described in, e.g., page 3814 of xe2x80x9cMultielectron Beam Blanking Aperture Array System SYNAPSE 2000xe2x80x9d by Hiroshi Yasuda, Soichiro Arai, Ju-ichi Kai, Yoshihisa Ooae, Tomohiko Abe, Shigeru Maruyama, and Takashi Kiuchi, J. Vac. Sci. Tech. Bulletin 14(6), November/December 1996; and page 185 of xe2x80x9cA High Speed EBL Column Designed to Minimize Beam Interactionsxe2x80x9d by Lee Veneklasen, J. Vac. Sci. Tech. B3(1), January/February 1985. However, use of an opening, among multiple openings in a single aperture plane, requires deflection of an incident charged particle beam by a large angle. The larger the angle of beam deflection, the more errors that are introduced in beam positioning, and the larger the errors in beam shaping. Further, the larger the required deflection angle, the slower the throughput.
Thus what is needed is a beam shaping system capable of patterning non-rectangular primitives with a reduced number of flashes and lower deflection angles to increase throughput of patterns having non-orthogonal sides.
An embodiment of the present invention includes a charged particle beam column for generating a variable shaped charged particle beam, the charged particle beam column including: a source of the charged particle beam; a first aperture defining a first opening positioned coaxial to the beam and spaced apart from the source; a second aperture defining a second opening positioned coaxial to the beam and spaced apart from the first aperture; a third aperture defining a third opening positioned coaxial to the beam and spaced apart from the second aperture; an imaging device coaxial to the beam, where the imaging device controls focusing of the beam; and at least two deflection devices coaxial to the beam which controls a path of the beam through the openings.
Thereby an embodiment of the present invention includes a method for shaping a charged particle beam, the method including the acts of: generating a charged particle beam; shaping the charged particle beam through a first opening; shaping the charged particle beam through a second opening; and shaping the charged particle beam through a third opening.
The present invention will be more fully understood in light of the following detailed description taken together with the accompanying drawings.